Ankylosing spondylitis

Introduction

Seronegative inflammatory disease of unknown aetiology primarily affecting younger men. Peripheral joint involvement is less common than spinal disease. The hip joint is involved in 30%–50% patients and is usually bilateral (50%–90%). Typical age of onset is 15–25 years. The younger the age at onset the more severe the disease is likely to be and the more likely the need for THA.

History

As for any inflammatory joint disease, the onset is often insidious and patients typically cannot give a precise time of onset or even pinpoint the initially affected side.

Clinical features

Early on the patient has a “hang-dog posture” (rounding of the shoulders and slight dorsal kyphosis). There is a loss of lumbar lordosis and limited spinal movements in all planes. Later, an advanced stoop develops, with limitation of forward vision (question mark posture). The chin brow angle, occiput to wall distance and gaze angle are used to evaluate functional deformity involving the cervical spine. There is severe loss of motion at the hip joint, a fixed flexion deformity or ankylosis. There is also reduced chest expansion.

Radiographs

Radiographs show ossification of the ligamentous origins and insertions about the trochanters, iliac crest and ischial tuberosities. Later on radiographs become similar to those for end-stage primary osteoarthritis.

Management options

If there is any uncertainty about whether the pain is arising from the hip joint or the spine then a local anaesthetic injection into the hip joint may be useful.